Containers have long been employed to store and transfer perishable food prior to presenting the food at a market where it will be purchased by the consumer. After perishable foods, such as meats, fruits, and vegetables, are harvested, they are placed into containers to preserve those foods for as long as possible. Maximizing the time in which the food remains preserved in the containers increases the profitability of all entities in the chain of distribution by minimizing the amount of spoilage.
The environment around which the food is preserved is a critical factor in the preservation process. Not only is maintaining an adequate temperature important, but the molecular and chemical content of the gases surrounding the food is significant as well. By providing an appropriate gas content to the environment surrounding the food, the food can be better preserved when maintained at the proper temperature or even when it is exposed to variations in temperature. This gives the food producer some assurance that after the food leaves his or her control, the food will be in an acceptable condition when it reaches the consumer.
Modified atmosphere packaging systems for one type of food, raw meats, exposes these raw meats to either extremely high levels or extremely low levels of oxygen (O.sub.2). Packaging systems which provide extremely low levels of oxygen are generally preferable because it is well known that the fresh quality of meat can be preserved longer under anaerobic conditions than under aerobic conditions. Maintaining low levels of oxygen minimizes the growth and multiplication of aerobic bacteria. Heretofore, low-level oxygen systems, such as the systems proposed in U.S. Pat. No. 3,574,642 to Weinke and U.S. Pat. No. 5,115,624 to Garwood, have obtained extremely low levels of oxygen by relying solely upon oxygen evacuation techniques to initially reduce the oxygen level around the raw meat to approximately zero percent.
In typical prior art systems, a package composed of flexible or rigid gas barrier materials is loaded into an evacuation chamber. The package in the evacuation chamber is subjected to a vacuum which reduces the oxygen level to approximately zero percent. After the package is evacuated, the raw meat either can be maintained in a "zero" atmosphere environment (commonly referred to as vacuum packaging) or can be refilled with a gas or mixture of gases to provide a modified atmosphere environment. To provide a modified atmosphere environment, the air-evacuated package is typically filled with a mixture of gases consisting of about 30 percent carbon dioxide (CO.sub.2) and 70 percent nitrogen (N.sub.2). Refilling the air-evacuated package with such a mixture of gases is believed to suppress the growth of aerobic bacteria. At this point the package is sealed. The meat in the modified atmosphere package takes on a less desirable purple-red color which few consumers would associate with freshness. This purple-red color, however, quickly "blooms" to a bright red color generally associated with freshness when the package is opened to oxygenate the fresh meat by exposure to air. The package is typically opened immediately prior to display of the fresh meat to consumers so as to induce blooming of the fresh meat just prior to display to the consumers.
Low-level oxygen systems relying solely upon evacuation techniques to diminish the oxygen level to approximately zero percent suffer from several disadvantages. For example, such systems operate at exceptionally slow speeds because they rely solely upon the use of an evacuation device along the packaging line to reduce the oxygen level to zero percent. The evacuation process is time-consuming, and the manufacture of the package cannot be completed until after the package has been fully evacuated. Furthermore, the evacuation techniques render it difficult to remove any oxygen within a previously wrapped package, such as an overwrapped meat tray, without creating vents in the package to allow the oxygen to escape. Trapped oxygen raises the residual oxygen level in the package and can also cause billowing and subsequent damage to the package during evacuation.
A need therefore exists for a system and method of making a modified atmosphere package which overcomes the aforementioned shortcomings associated with existing techniques of making those packages.